Solid-state polymeric materials based on oxygen-sensitive photoluminescent dyes are widely used as optical oxygen probes. See, for example United States Published Patent Applications 2009/0029402, 2008/8242870, 2008/215254, 2008/199360, 2008/190172, 2008/148817, 2008/146460, 2008/117418, 2008/0051646, 2006/0002822, U.S. Pat. Nos. 7,569,395, 7,534,615, 7,368,153, 7,138,270, 6,689,438, 5,718,842, 4,810,655, and 4,476,870. Such optical probes are available from a number of suppliers, including Presens Precision Sensing, GmbH of Regensburg, Germany, Oxysense of Dallas, Tex., United States, and Luxcel Biosciences, Ltd of Cork, Ireland.
Such probes may be interrogated through many common packaging materials and therefore allow nondestructive measurement of the oxygen concentration within an enclosure by simply incorporating a probe within the packaging, typically adhered to the inside surface of the cover. Unfortunately, there are certain applications where incorporation of such a probe into the packaging is not acceptable—such as packages made from materials that interfere with interrogation of the probe, packages in which the presence of such a probe inside the packaging may be mistakenly perceived by consumers as an undesired contamination of the packaged product, or packages whose per package value or profit margin cannot accommodate the cost of incorporating a probe into every package or tracking those containing a probe when only select packages include a probe.
Hence, a need exists for a probe that can nondestructively sense the oxygen concentration within an enclosure from outside the enclosure.